The basic objective of this project is to determine how tetrapyrroles are biosynthesized in the strict anaerobe Desulfovibrio. Tetrapyrroles constitute an important class of biomolecules that function in diverse roles at the active site of many processes critical to cellular metabolism. As hemes, chlorophylls, vitamins, and Ni-cofactors, they are well known prosthetic groups essential for their catalytic properties. Desulfovibrio possess a high content of diverse electron transport hemoproteins. It has high tetrapyrrole biosynthesis activity in order to meet the requirements for these essential prosthetic groups, and therefore is an excellent microbial model system for the general area of tetrapyrrole production. Elucidation of the biosynthetic pathways to these hemes with an emphasis on characterizing the enzymes responsible for specific biotransformations of intermediates will provide fundamental knowledge toward understanding how high rates of tetrapyrrole biosynthesis can be achieved. The specific aims fall into two categories. Tetrapyrrole intermediates will be isolated and their chemical structures determined by a combination of optical, mass, and NMR spectroscopic techniques. Then enzymes responsible for the conversions of uroporphyrinogen into protoporphyrin IX and siroheme will be purified by conventional techniques of protein purification. Their physiochemical and enzymatic properties will be measured. Preliminary data to be discussed indicates that the Desulfovibrio biosynthetic system differs in several key ways from more conventional ones.